The present invention is related to bonding or welding of soft tissue and, more particularly, to a system and method for controlling tissue welding.
RF electrosurgical tools are widely used in a variety of medical applications for cutting, soft tissues, hemostasis and various cauterization procedures. Currently-available electrosurgical bipolar instruments generally use two electrodes of opposite polarity, one of which is located on each of the opposite jaws of, for example, a grasper. In use, tissue is held between the electrodes and alternating RF current flows between the two electrodes, heating the tissue. When the tissue temperature reaches about 50-55xc2x0 C., denaturation of albumens occurs in the tissue. The denaturation of the albumens results in the xe2x80x9cunwindingxe2x80x9d of globular molecules of albumen and their subsequent entangling which results in coagulation of the tissues. Once the tissue is treated in this way, the tissue can be cut in the welded area with no bleeding. This process is commonly referred to as bipolar coagulation.
Tissue welding generally comprises bringing together edges of an incision to be bonded, compressing the tissue with a bipolar tool and heating the tissue by the RF electric current flowing through them. One of the major differences between tissue welding procedures and coagulation with the purpose of hemostasis is that tissue welding requires conditions which allow for the formation of a common albumen space between the tissue to be bonded before the beginning of albumen coagulation. If such conditions are not present, coagulation will take place without a reliable connection being formed.
Problems which can occur during the tissue welding process include thermal damage to adjacent structures, over-heating of tissue and under-coagulation. Over-heating of tissue results in delayed healing, excessive scarring, tissue charring/destruction, and in tissue sticking to the electrosurgical tool. If tissue sticks to the electrosurgical tool upon removal, the tissue can be pulled apart at the weld site, adversely affecting hemostasis and causing further injury. Under-coagulation can occur if insufficient energy has been applied to the tissue. Under-coagulation results in weak and unreliable tissue welds, and incomplete hemostasis.
Precise control of the welding process while avoiding excessive thermal damage, over-heating or under-coagulation is a difficult process, particularly when attempting to weld tissue of varying structure, thickness and impedance. The problem of crating a viable automatic control system is particularly important for welding whose purpose is recovery of physiological functions of the organs operated on. After hemostasis, vessels or vascularized tissue parts which have been heated typically do not recover and lose functionality.
Prior attempts to automate the control of tissue coagulation have met with limited success. Attempts to avoid over-heating include the use of electrosurgical tools with built-in temperature measuring devices. Built-in temperature measuring devices are used to measure the tissue temperature, provide feedback and thereby, prevent overheating. However, use of built-in temperature sensors causes the electrosurgical tools to be cumbersome, while providing only limited or inaccurate information about the status of the inner layers of the tissue between the electrodes where a connection is potentially being formed.
Several prior art references suggest various methods of using the tissue impedance and a minimum tissue impedance value to define a point when coagulation is completed and tissue heating should be discontinued. Other references suggest use of a relationship between tissue impedance and current frequency to detect a point of coagulation.
The prior art methods, however, do not provide effective tissue bonding solutions for use in surgical procedures and specifically lack the ability to adapt to varying tissue types and thickness during the welding procedure.
It would therefore be desirable to provide an electrosurgical system and method suitable both for tissue bonding and for hemostasis which allows for adaptation to varying tissue types, structure, thickness, and impedance without over-heating, while providing a reliable tissue connection. Such a system and method would significantly reduce the time needed for surgical procedures involving tissue welding by eliminating the need for equipment adjustment during the welding process.